Process for the inhibition of scale in harsh systems and novel antiscalants for same

ABSTRACT

The present invention provides a novel class of polymer antiscalants which are polymers comprising a 1,2-dihydroxy-3-butene monomer unit and at least one monomer unit derived from the groups consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid, and salts thereof, with the proviso that said polymers do not contain the monomer unit —(CH 2 —CH═CH—CH 2 —O)—.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This application is a divisional of U.S. Pat. Application No.09/144,145, filed Aug. 31, 1998, entitled, “Process For the Inhibitionof Scale in Harsh Systems and Novel Antiscalants For Same”, now U.S.Pat. No. 6,146,495.

This invention relates to a process for the inhibition of scaleformation in aqueous systems which are generally maintained under harshconditions. The invention more particularly relates to an improved kraftprocess wherein calcium carbonate scale in inhibited. In one specificaspect of this invention, there is provided novel polymeric antiscalantswhich are useful in the preclusion of calcium carbonate scaling inindustrial aqueous systems.

BACKGROUND OF THE INVENTION

Scale forms when the concentration of a dissolved mineral exceeds itssolubility limit and the mineral precipitates. Scale is and can be aproblem in equipment used in many types of industrial operationsutilizing an aqueous system.

As used herein the term “aqueous system” is meant to include any systemcontaining water, including but not limited to cooling water, boilerwater, desalination, gas scrubbers, blast furnaces, sewage sludgethermal conditioning equipment, reverse osmosis evaporators, paperprocessing, mining circuits and the like wherein such systems areoperated under harsh conditions of temperature and pH.

The term “harsh conditions” as used herein is intended to be definitiveof an aqueous system wherein the temperature is in the range of fromabout 100° C. to about 200° C. and the pH is in the range of from about10 to about 14.

Typical equipment used in industrial aqueous operations that requirescale inhibition includes, but is not limited to, boilers, evaporators,heat exchangers, other heat transfer equipment, pipes and any otherequipment that comes into contact with the aqueous system.

For purposes of this application, such industrial operations areillustrated by the kraft process for the production of wood pulp.

Wood pulp is the basic raw material used in the manufacture of almostall grades of paper and various types of packing products such as drumsand cartons.

In order to produce pulp from wood, it is necessary to separate thecellulose fibers from the various organic compounds, mainly lignin,which bind them together. Various mechanical and chemical methods areused to effect this separation, but the most widely used technique isknown as the kraft or sulphate process, since it produces pulp whichgives high strength and good aging properties to paper products.

In the kraft process, a cooking liquor (white liquor) of sodiumhydroxide and sodium sulphide is used to extract the lignin from wood.The process of extraction is carried out in digesters, either batch orcontinuous. The pH in the digester is generally between about 11 andabout 14.

The liquor temperature is maintained between about 150° to about 175° C.A period of from about 2 to about 3 hours is usually required forcomplete digestion. The pulp is then washed before being sent forfurther treatment such as bleaching prior to its further use.

The economics of the kraft process depend on the recovery of the cookingliquor. In this recovery process, the digestion chemicals contained inthe used cooking liquor (black liquor) are recovered via evaporators,furnaces and a causticizer for reuse in preparing new cooking liquor.Before the black liquor can be used as a feed it is necessary that theblack liquor be concentrated, usually to 45% by weight or higher. Thisconcentration is carried out in a multiple-effect evaporator, where livesteam is introduced to the first unit (where the liquor is at itshighest solids concentration) and flows to the final unit. Suchevaporators can be described as one long heat transfer surface where thepurpose is to boil off water by providing significant contact betweenthe black liquor and steam heated surfaces. However, a common problemwhich is experienced in such evaporators is the formation of substantialamounts of deposits which tend to stick to the interior walls or tubesof the evaporator. The primary source of liquor scaling in theevaporator system is insoluble calcium carbonate.

The cooking liquor (white liquor) produced from this process containssodium hydroxide, sodium sulphide and sodium carbonate due to incompletereaction in the causticizer, as well as soluble calcium and precipitatedcalcium carbonate.

In the kraft process, calcium is extracted from the wood, and because ofthe high pH, temperature and presence of carbonate in the cooking liquorthis calcium precipitates as calcium carbonate. The most visible form ofthe scale is in the cooking liquor heaters which maintain desireddigester process conditions and often have to be cleaned about every 2-4weeks.

Scale formation can also occur on the liquor separator screens which inturn leads to a restriction of liquor flow which reduces plantproduction and eventually necessitates plant shutdown for cleaning.

Because of the tendency for calcium carbonate scaling in the aqueoussystems of the kraft process due to the conditions experienced therein,there becomes a real need for the addition of antiscalants to variouslocations within the process.

In addition to the scaling problem experienced in the digester, scalingis also a problem in the equipment used for carrying out the bleachingof the wood pulp. Pulp produced by the kraft process is normallybleached in a multistage sequence to obtain the desired brightness andstrength. Different bleaching agents are used for this purpose. Chlorineor chlorine dioxide is the most reactive bleaching agent to the ligninremaining in the pulp. Although conditions in the bleach plant are lesssevere than those found in a kraft digester, the driving force for scaleformation is significant. For example, calcium concentrations can climbto over 100 ppm, the pH of the stream entering the bleaching stages isgreater than about 11 and the temperatures are still elevated.

From the foregoing, it can be seen that while conditions vary inseverity with various stages of the kraft process i.e. the digester,bleach plant and evaporator, such aqueous systems as are containedwithin the various stages are all under harsh conditions of temperatureand pH and as such experience the problem of scale formation duringoperation.

Thus, it becomes readily apparent that there is a real need in the kraftprocess for the production of wood pulp which comprises the steps ofdigesting wood chips in a digesting zone, bleaching of the resultingwood pulp in a bleaching zone and the concentrating of the separatedliquor from the digesting zone in an evaporation zone for the providingof an improvement thereto which comprises the addition of a polymericantiscalant which will inhibit the formation of scale.

Accordingly, it is an object of the present invention to provide a novelprocess for the inhibition of calcium carbonate scale in aqueous systemswhich otherwise experience such scale formation due the harsh conditionsoccurring in the system.

Another object of the present invention is to provide a process forimproving the kraft process for the production of wood pulp wherein theformation of calcium carbonate scale is inhibited during plantoperations.

A still further object of this invention is to provide novel polymericantiscalants for use in the treatment of industrial aqueous systems.

Other aspects, objects and the several advantages of this invention willbecome apparent in light of the following specification and appendedclaims.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, we havediscovered a process for treating an aqueous liquid having scale formingsalts of calcium therein which comprises adding to said aqueous liquid ascale inhibiting amount of a polymeric antiscalant comprising:

(A) 1,2-dihydroxy-3-butene monomer units and,

(B) at least one monomer unit derived from the group consisting ofmaleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid,vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide,butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethylpropane sulfonic acid, and salts thereof, with the proviso that saidpolymers does not include the monomer unit —(CH₂—CH═CH—CH₂—O)—.

In another embodiment of the present invention, there is provided animproved kraft process for the production of wood pulp using novelpolymer antiscalants.

Thus, in the kraft process for the production of wood pulp whichcomprises the steps of digesting wood chips in a digesting zone,bleaching the resulting wood pulp in a bleaching zone, and concentratingthe separated liquor from the digesting zone in an evaporation zone,there is provided the improvement which comprises adding to at least oneof said digesting zone, bleaching zone and evaporation zone a polymericantiscalant in an amount sufficient to inhibit the scale formationtherein, said antiscalant comprising:

(A) at least one monomer unit derived from the group consisting of1,2-dihydroxy-3-butene, N-(hydroxymethyl) acrylamide and N-(sulfomethyl)acrylamide and,

(B) at least one monomer unit derived from the group consisting ofmaleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid,vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide,butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethylpropane sulfonic acid, and salts thereof.

In a still further embodiment of the present invention, there areprovided novel polymers comprising:

(A) 1,2-dihydroxy-3-butene monomer units and

(B) at least one monomer unit derived from the groups consisting ofmaleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid,vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide,butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethylpropane sulfonic acid, and salts thereof, with the proviso that saidpolymers do not include the monomer unit —(CH₂—CH═CH—CH₂—O)—.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based upon our discovery that calcium carbonateis scale in aqueous systems which experience harsh conditions oftemperature and pH can be inhibited by the addition to such systems ascale inhibiting amount of a polymeric antiscalant comprising:

(A) at least one monomer unit derived from the group consisting of1,2-dihydroxy-3-butene, N-(hydroxymethyl) acrylamide and N-(sulfomethyl)acrylamide and,

(B) at least one monomer unit derived from the group consisting ofmaleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid,vinyl sulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide,butoxymethylacrylamide, N,N-dimethylacrylamide, sodium acrylamidomethylpropane sulfonic acid, and salts thereof

Such polymeric antiscalants have a weight average molecular weight (Mw)in the range of from about 1,000 to about 100,000, preferably from about1,000 to about 50,000. For purposes of this application, all weightaverage molecular weights are measured by aqueous gel permeationchromatography (GPC) relative to either a polyethylene glycol standardor a polystyrene sulfonate standard.

The amount of polymeric antiscalant which is employed in the practice ofthis invention is dependent on the nature of the system being treated.In carrying out the process of scale inhibition in accordance with thepresent invention, the selected polymeric antiscalant is added to theaqueous system to be treated in an amount sufficient to preclude scaleformation, deposition on or adherence to the metallic surfaces of thesystem being treated. In general, effective amounts of the selectedpolymeric antiscalant are in the range of from about 1 ppm to about 200ppm.

The polymeric antiscalants, as employed in the process of thisinvention, can be used alone or in combination with other known scaleinhibitors and dispersing agents which are stable under the conditionsprevailing in the system being treated. However, such additional scaleinhibitors are not required in obtaining satisfactory results whencarrying out the process of the present invention using the polymericantiscalants as described herein.

The particular dosage of polymeric antiscalant will be dependent uponthe conditions which are normally experienced in the system beingtreated. Thus, in the kraft process, the highest dosage levels ofpolymeric antiscalant will be to the digester with lesser amounts beingrequired for the bleach plant and evaporator.

In the practice of a presently preferred embodiment of this invention,whereby there is achieved an improvement in the kraft process forproduction of wood pulp through the addition to the digester, bleachplant or evaporator of polymeric antiscalants as herein defined, suchaddition of the selected antiscalant can be carried out by any meansknown in the art for addition of antiscalants to a harsh environment.For example, a solution of the selected antiscalant can be continuouslyintroduced into the digester in amounts sufficient to achieve thedesired concentration level. Not only does addition at this stage serveto preclude scaling in the digester, it permits antiscalant to becarried over to the washers from which the pulp is screened and cleaned.In addition to the addition of the antiscalants to the digester, suchantiscalants can also be introduced into one or more of the bleachingtowers, washers or caustic extraction towers which are normally providedin multiple stages to permit the desired chlorination and extraction soas to achieve delignification and ultimate brightening of the pulp.Likewise, since efficient recovery of chemicals from the digestor liquorand reconstitution of the chemicals to form fresh while liquor for usein the digester is desired, addition of one or more of the polymericantiscalants of this invention to the evaporators serving to concentratesuch liquor from the digestor for further use in the process will serveto reduce or preclude undesirable scaling in such equipment.

Thus, by treating one or more of the kraft process zones whereinundesired calcium carbonate scaling is otherwise experienced, there isachieved by the process of the present invention an overall improvementin the efficiency of the kraft process due to the inhibition of scaleformation which in turn permits longer operating periods.

A further embodiment of the present invention are a novel group ofpolymeric antiscalants which exhibit antiscalant properties whenemployed in aqueous systems having scale forming salts of calcium.

Such novel antiscalants are those polymers comprising1,2-dihydroxy-3-butene monomer units and at least one monomer unitderived from the group consisting of maleic acid, acrylic acid,acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid,styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide,N,N-dimethylacrylamide, sodium acrylamidomethyl propane sulfonic acid,and salts thereof, with the proviso that said novel polymers do notinclude the monomer unit —(CH₂—CH═CH—CH₂—O)—.

The novel antiscalant polymers can have a mole content of1,2-dihydroxy-3-butene from about 1 to about 50 percent of the totalmole percent in the polymer.

In one presently preferred embodiment of the present invention, thenovel antiscalant compositions are a 50 mole percent:50 mole percentcopolymer of 1,2-dihydroxy-3-butene and maleic acid having a molecularweight of approximately about 4,000; and a 33.3 mole percent:33.3 molepercent:33.3 mole percent terpolymer of 1,2-dihydroxy-3-butene, maleicacid and acrylic acid having a molecular weight of approximately 10,000.

Such novel polymeric antiscalants can be prepared by conventional freeradical polymerization in an aqueous media. Such processes are wellknown to those skilled in the art. In general, a typical conventionalfree radical polymerization process includes adding one or more monomersto a reaction vessel followed by neutralization with a suitable base.Polymerization catalysts may also be added to the vessel up-front or fedin gradually during the course of the reaction. Water soluble initiatorssuch as any free radical or redox initiator or combination thereof areadded along with any other optional monomer to the reaction mixture inseparate feeds over the same amount of time, usually 4 to 6 hours. Thereaction temperature is maintained from about 90° to about 100° C.Additional initiator may be used after addition is complete to reduceresidual monomer level. At the end of the reaction, a suitable base isadded to adjust pH.

1,2-dihydroxy-3-butene can be obtained from Eastman Chemical Company,Fine Chemicals, P.O. Box 431, Kingsport, TN 37662, (telephone number is1-800-327-8626) or it can be made synthetically by hydrolyzing epoxybutene.

EXAMPLES

The following examples are intended to be illustrative of the presentinvention and to teach one of ordinary skill how to make and use theinvention. These examples are not intended to limit the invention in anyway.

EXAMPLE I Autoclave Testing of Antiscalant Procedure for the Control ofCalcium Carbonate in kraft Digesters and Bleach Plants

In carrying out the tests of the various polymeric antiscalants, aconcentrated synthetic black liquor was prepared as follows.

In a 1000 mL beaker, 4 grams (g) of Na₂CO_(3,) 2 g of indulin AT(precipitated lignin) and 16 mL of 500 g/l NaOH were diluted to a volumeof 1000 mL using distilled water. The beaker was mixed on a stir plateuntil no precipitated lignin and sodium carbonate were detected. Thedissolved liquor was filtered with a 0.45 μm filter and transferred to a2000 mL graduated cylinder. The liquor was diluted to a final volume of2 liters.

5000 ppm actives based samples of the antiscalant chemistries andcalcium solutions were made. All the glassware and autoclaves were acidcleaned using a 10% solution of H₂SO_(4,) 16 B.U.N. tubes were filledwith 20 mL of double distilled water and placed in a test tube rackfilling a matrix or 8 columns and 2 rows. The autoclave digester waspreheated to a temperature of 50° C. (approximately 30 minutes). 25 mLof double distilled water and enough antiscalant solution to produce thedesired actives concentrations in 100 mL were added to eight 100 mLvolumetric flasks. 50 mL of the concentrated black liquor and 2 mL of5000 ppm calcium solution were added to each flask and the flasks werebrought up to 2 mL below the fill line. The flasks were hand mixed toredissolve any precipitate which formed upon addition of calcium. Thecontents (100 mL) of the flask were transferred to the autoclaves(Lorentzen & Wettre autoclaves). 2 mL of the sample were transferred tothe B.U.N. tubes for the estimation of initial calcium concentration.The autoclaves were sealed with a wrench and the autoclave heater wasset as per the desired temperatures. The autoclaves were rotated andheating was begun and the samples were lowered into the hot oil bath.Effect on inhibition of calcium carbonate precipitation in the kraftdigester was evaluated at 170° C. for 30 minutes. For the bleach plantscreening, the samples were allowed to reach 100° C. and run for 30minutes at that temperature. The heating was turned off and the sampleswere raised out of the oil bath. The autoclaves were cooled for 10minutes in a tub of cold water immediately after removal. The autoclaveswere opened and 2 mL of this liquor was filtered through a 0.45 μmsyringe filter and transferred to the B.U.N. test tubes for theestimation of final calcium. The B.U.N. tubes were all brought up to the25 mL line using double distilled water and parafilm was placed over thetop. The samples were hand mixed. The calcium levels were measured usingatomic absorption using calibrated standards. The percent scaleinhibition is expressed as below:${\% \quad {Inhibition}} = {\frac{{filtered}\quad {calcium}}{{initial}\quad {calcium}}*100}$

The following results were obtained.

It is understood that for each test run, the results given for BLANK (noantiscalant) are not an example of the invention, but rather they arecomparative examples.

In the kraft Digester % Inhibition at Various Additive ConcentrationsBlank (no antiscalant) 4.4 4.4 Polymer (antiscalant) 50 ppm 100 ppm50:50 copolymer of 8.4 16 1,2-dihydroxy-3-butene, maleic acidSulfomethylated 6.3 10 poly(maleic acid, acrylic acid) In the BleachPlant % Inhibition at Various Additive Concentrations Blank (noantiscalant) 10 10 Polymer (antiscalant) 50 ppm 100 ppm 33.3:33.3:33.325 62 terpolymer of 1,2-dihydroxy-3-butene, maleic acid, acrylic acid50:50 copolymer of 52 60 1,2-dihydroxy-3-butene, maleic acidSulfomethylated 34 67 poly(maleic acid, acrylic acid) 45:45:10terpolymer of 40 62 maleic acid, acrylic acid, N-hydroxymethylacrylamide

EXAMPLE II Evaluation of Antiscalant Chemistries for Controlling Scalein Black Liquor Evaporators

A 12″ long Teflon® reactor with an inside diameter of 1.5″ and anoutside diameter of 2″ was used in these screening experiments. A 0.25″cartridge heater (600 W) was inserted into the reactor bottom via abored 0.5″ threaded reducing bushing that was screwed into the bottomTeflon® endcap. A stainless steel adapter attached to the top endcap wasused to seat the 24/40 ground-glass joint of a reflux condenser, with aTeflon® sleeve inserted to facilitate sealing of the groundglass-stainless connection. The cooking was carried at 100° C. for 60minutes. The remaining experimental procedure was followed in accordancewith the directions outlined in the kraft digesters and bleach plantsscreening test procedure of Example I.

The following results were obtained.

Summary of Screening Result for the Control of Calcium Carbonate Scalingin the Black Liquor Evaporators % Inhibition at Various PolymerConcentrations Blank (no antiscalant) 10 10 Polymer (antiscalant) 100ppm 200 ppm 45:45:10 maleic acid, 38 99 acrylic acid, N-hydroxymethylacrylamide 33.3:33.3:33.3 terpolymer 69 95 maleic acid, acrylic acid,1,2-dihydroxy-3-butene 50:50 copolymer maleic 37 72 acid,1,2-dihydroxy-3-butene Sulfomethylated poly 63 100  (maleic acid,acrylic acid)

EXAMPLE III Preparation of a 33.3 mole percent Acrylic Acid/ 33.3 molepercent Maleic Acid/ 33.3 mole percent 1,2 Dihydroxy-3-buten Terpolymer

To a 5-neck, 100 mL resin flask equipped with a mechanical stirrer,reflux condenser, and syringe pumps for continuous addition of monomersand initiators were charged 10.7 g of distilled water, 12.74 g of maleicanhydride, 20 g of a 57 weight percent solution of1,2-dihydroxy-3-butene, and 12.48 g of 50 weight percent aqueoussolution of sodium hydroxide using cooling to control any exotherm. Themixture was then heated to approximately 98° C. At temperature, 0.67 gof a 0.15 percent solution of iron sulfate heptahydrate dissolved indistilled water was added to the reaction mixture. Next, 1.87 g ofacrylic acid were added to the reactor followed by 0.34 g of aninitiator solution consisting of 0.145 g sodium persulfate, 1.06 g of a30 weight percent hydrogen peroxide solution, and 4 g of distilledwater. The remaining initiator solution and a solution of 7.5 g ofacrylic acid and 2.22 g of distilled water, were then fed separatelyinto the flask at a constant rate over a period of approximately 4.5hours while the reaction temperature was held between 90° C. and 100° C.After monomer and initiator feeding was complete, the reaction was heldat temperature for an additional 30 minutes. An additional initiatorsolution consisting of 9.86 g of a 30 weight percent hydrogen peroxidesolution, 1.31 g of sodium persulfate, and 5 g of distilled water wasthen fed into the reactor over a period of 3 hours, and again held afteraddition for 30 minutes. The reaction was cooled to 80° C., and asolution of 1.02 g of sodium metabisulfite and 3.63 g of distilled waterwas added over a half hour period. The reaction mixture was held attemperature for an additional 30 minutes and then cooled to roomtemperature. ¹³CNMR confirmed product formation. The product had aweight average molecular weight of approximately 10,000, as measured bygel permeation chromatography (GPC) using polyethylene glycol (PEG) MWstandards.

EXAMPLE IV Preparation of a 50 mole percent Maleic Acid/ 50 mole percent1,2-Dihydroxy-3-butene Copolymer

To the reactor described in Example III were charged 15 g of distilledwater, 15.39 g of maleic anhydride, 24.24 g of a 57 weight percentsolution of 1,2-dihydroxy-3-butene, and 13.80 g of a 50 weight percentaqueous solution of sodium hydroxide using cooling to control anyexotherm. The mixture was then heated to approximately 98° C. Attemperature, an initiator solution consisting of 2.57 g of sodiumpersulfate, 18.86 g of a 30 weight percent hydrogen peroxide solution,and 5.49 g of distilled water was then fed into the flask at a constantrate over a period of approximately 4.5 hours while the reactiontemperature was held between 90° C. and 100° C. After monomer andinitiator feeding was complete, the reaction was held at temperature foran additional 30 minutes. The reaction was then cooled to 80° C., and asolution of 1.02 g of sodium metabisulfite and 3.63 g of distilled waterwas added over a half hour period. The reaction mixture was held attemperature for an additional 30 minutes and then cooled to roomtemperature. ¹³CNMR confirmed product formation. The product had aweight average molecular weight of approximately 4,000, as measured bygel permeation chromatography (GPC) using polyethylene glycol (PEG) MWstandards.

The specific examples herein disclosed are to be considered as beingprimarily illustrative. Various changes beyond those described, will, nodoubt, occur to those skilled in the art; and such changes are to beunderstood as forming a part of this invention insofar as they fallwithin the spirit and scope of the appended claims.

We claim:
 1. Polymers comprising: (A) 1,2-dihydroxy-3-butene monomerunits and (B) at least one monomer unit is selected from the groupsconsisting of maleic acid, acrylic acid, acrylamide, methacrylic acid,itaconic acid, vinyl sulfonic acid, styrene sulfonic acid,N-tertbutylacrylamide, butoxymethylacrylamide, N,N-dimethylacrylamide,sodium acrylamidomethyl propane sulfonic acid, and salts thereof, withthe proviso that said polymers do not contain the monomer unit—(CH₂—CH═CH—CH₂—O)—.
 2. Polymers of claim 1 having a weight averagemolecular weight in the range of from about 1,000 to about 100,000. 3.Polymers of claim 1 having a weight average molecular weight in therange of from about 1,000 to about 50,000.
 4. Polymers of claim 1wherein the mole percent of (A) is in the range of from about 1 to 50percent of the total mole percent of monomer units in the polymer. 5.Polymers of claim 1 wherein (B) is derived maleic acid.
 6. Polymers ofclaim 1 wherein (B) is a mixture of maleic acid and acrylic acid.
 7. Apolymer of claim 5 wherein the mole ratio of (A) and (B) in the polymeris 50:50.